tour: check if file content is set before storing in localStorage

file() returns undefined when there is no file to display, like on
https://tour.golang.org/welcome/2

Change-Id: Ia26719537949c9909947068d790f07e2eee8f9ff
Reviewed-on: https://go-review.googlesource.com/90075
Reviewed-by: Andrew Bonventre <andybons@golang.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/static/js/controllers.js b/static/js/controllers.js
index e035544..c64fb04 100755
--- a/static/js/controllers.js
+++ b/static/js/controllers.js
@@ -22,7 +22,7 @@ controller('EditorCtrl', ['$scope', '$routeParams', '$location', 'toc', 'i18n',
                 var f = file();
                 return f && f.Content;
             }, function(val) {
-                storage.set(file().Hash, val);
+                if (val) storage.set(file().Hash, val);
             });
         });